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Abstract:

A method for determining a parameter representative of the state of
vigilance of a vehicle driver, from the measurement of the steering wheel
angle of the vehicle includes determining two successive ranges of
temporal windows: a first range of temporal windows T(t1) extending
between ti and ti-t1 with t1min≦t1≦t1max, and a second
range of temporal windows T(t2) extending between ti-t1 and ti-t1-t2,
with t2min≦t2≦t2max, the two ranges of temporal windows
T(t1), T(t2) are scanned and for each of the temporal windows T(t1),
T(t2), a datum v(t1), v(t2) is calculated representative of the
dispersion of the steering wheel angle values measured during the
temporal window. Finally, for each pair of temporal windows T(t1)-T(t2),
the ratio v(t1)/v(t2) is calculated, and the ratio v(t1)/v(t2) with the
maximum value is selected as the value representative of the state of
vigilance of the driver.

Claims:

1. A method for determining a parameter representative of the state of
vigilance of a vehicle driver, from the measurement of the steering wheel
angle of said vehicle, characterized in that it consists, at each
sampling instant ti, in: determining two ranges of successive temporal
windows: a first range of temporal windows T(t1) extending between ti and
ti-t1 with t1min≦t1.ltoreq.t1max, and a second range of temporal
windows T(t2) extending between ti-t1 and ti-t1-t2, with
t2min≦t2.ltoreq.t2max, scanning the two temporal window ranges
T(t1), T(t2) by varying the values t1 and t2 between their minimum and
maximum values, and calculating, for each of the temporal windows T(t1),
T(t2), a datum respectively v(t1), v(t2) representative of the dispersion
of the values of the steering wheel angle measured during said temporal
window, calculating, for each pair of temporal windows T(t1)-T(t2), the
ratio v(t1)/v(t2) of the corresponding values v(t1), v(t2), and selecting
as the value representative of the state of vigilance of the driver at
instant ti, the ratio v(t1)/v(t2) with the maximum value.

2. The method as claimed in claim 1, characterized in that: the first
range of temporal windows T(t1) extends between a minimum duration
adapted to allow approximately 5 measurements of the steering wheel angle
and a maximum duration adapted to allow approximately 200 measurements of
the steering wheel angle, the second range of temporal windows T(t2)
extends between a minimum duration adapted to allow approximately 30
measurements of the steering wheel angle and a maximum duration adapted
to allow approximately 80 measurements of the steering wheel angle.

3. The method as claimed in claim 1, characterized in that the datum
v(t1), v(t2) representative of the dispersion of the measured values of
the steering wheel angle consists of the variance of said values.

4. The method as claimed in claim 1, characterized in that the sampling
frequency is 10 Hertz.

5. The method as claimed in claim 2 characterized in that the datum
v(t1), v(t2) representative of the dispersion of the measured values of
the steering wheel angle consists of the variance of said values.

6. The method as claimed in claim 2 characterized in that the sampling
frequency is 10 Hertz.

7. The method as claimed in claim 3 characterized in that the sampling
frequency is 10 Hertz.

Description:

[0001] The invention relates to a method for determining a parameter
representative of the state of vigilance of a vehicle driver.

[0002] When analyzing the behavior of drivers, it has been established
that a phase of activity following a phase of relative inactivity could
prove representative of a lowering of vigilance of the driver. These
findings have been chiefly used for implementing a method for determining
a parameter representative of the state of vigilance of a driver
disclosed in patent EP1548678, based on measurements of the steering
wheel angle and determining the ratio of variances of these values for
two successive temporal windows each having a predetermined duration.
However, notably because of the difficulties of determining the
parameters necessary for its implementation (size of temporal windows,
etc.), this method proves to be of very limited accuracy and therefore
reliability.

[0003] The present invention is aimed at overcoming this drawback and has
as its main objective to provide a reliable and accurate method for
determining a parameter representative of the state of vigilance of a
driver from the measurement of the steering wheel angle of a vehicle.

[0004] To this end, the invention is aimed at a method for determining a
parameter representative of the state of vigilance of a vehicle driver,
from the measurement of the steering wheel angle of said vehicle, said
method consisting, at each sampling instant ti, in: [0005] determining
two ranges of successive temporal windows: a first range of temporal
windows T(t1) extending between ti and ti-t1 with
t1min≦t1≦t1max, and a second range of temporal windows
T(t2) extending between ti-t1 and ti-t1-t2, with
t2min≦t2≦t2max, [0006] scanning the two temporal window
ranges T(t1), T(t2) by varying the values t1 and t2 between their minimum
and maximum values, and calculating, for each of the temporal windows
T(t1), T(t2), a datum respectively v(t1), v(t2) representative of the
dispersion of the values of the steering wheel angle measured during said
temporal window, [0007] calculating, for each pair of temporal windows
T(t1)-T(t2), the ratio v(t1)/v(t2) of the corresponding values v(t1),
v(t2), and selecting as the value representative of the state of
vigilance of the driver at instant ti, the ratio v(t1)/v(t2) with the
maximum value.

[0008] Such a method, at each sampling, leads to determining the pair of
temporal windows T(t1), T(t2) corresponding to the highest ratio of
values representative of the dispersion of measurements of the steering
wheel angle, i.e., for the period preceding the sampling, the datum most
representative of a possible quiet phase/active phase event.

[0009] This method can thus be used to limit the study of the ratio of the
values representative of the dispersion of measurements to the study of
its local maxima, and thus to detect the exact date of the quiet
phase/active phase event without further requiring the preliminary
setting of a threshold on the dispersion values or a size for the
temporal windows.

[0010] Such a method thus proves to lead, reliably and accurately, to
determining a parameter that is directly usable for assessing the state
of vigilance of a driver.

[0011] According to an advantageous embodiment of the invention, the first
range of temporal windows T(t1) extends between a minimum duration
adapted to allow approximately 5 measurements of the steering wheel angle
and a maximum duration adapted to allow approximately 200 measurements of
the steering wheel angle. Also advantageously, the second range of
temporal windows T(t2) extends between a minimum duration adapted to
allow approximately 30 measurements of the steering wheel angle and a
maximum duration adapted to allow approximately 80 measurements of the
steering wheel angle.

[0012] Thus with a sampling frequency having a value advantageously equal
to 10 Hertz, the range of temporal windows T(t1) extends between 500 ms
and 20 s while the range of temporal windows T(t2) extends between 3 s
and 8 s.

[0013] Moreover, the datum v(t1), v(t2) representative of the dispersion
of the measured values of the steering wheel angle advantageously and
ordinarily consists of the variance of said values.

[0014] The method according to the invention will be better understood
upon reading the following detailed description with reference to the
accompanying drawings which show:

[0015] FIG. 1, a curve representative of the variations over a period of a
few seconds of the steering wheel angle of a vehicle,

[0016] and FIG. 2, the corresponding curve of variations in the ratio of
variances determined according to the invention.

[0017] The method according to the invention disclosed below with
reference to the accompanying drawings consists of a method for
detecting, from measurements of the steering wheel angle of a vehicle
carried out with a sampling frequency of 10 Hertz, the sequence of a calm
phase followed by an active phase, i.e. a sequence as shown in FIG. 1 (in
which the abscissa scale is 1 second, and which thus represents the
change in the steering angle over a period of 8 seconds).

[0018] According to this method and in the first place, two ranges of
successive temporal windows are determined: one range of temporal windows
T(t1) extending between 500 ms and 20 s and one range of temporal windows
T(t2) extending between 3 s and 8 s.

[0019] At each sampling instant ti, this method consists in scanning the
two ranges of temporal windows by varying the range T(t1), starting from
ti, between a minimum value of 500 ms and a maximum value of 20 s, and
the range T(t2), starting from ti-t1, between a minimum value of 3 s and
a maximum value of 8 s.

[0020] The calculation of the variances v(t1), v(t2) of the steering wheel
angle values obtained for each temporal window can then be used to
determine the highest v(t1)/v(t2) ratio.

[0021] As shown in the figures, the successive samplings can be used to
obtain the curve shown in FIG. 2, which proves to constitute a faithful
picture of the variations in the steering wheel angle (amplitude, event
dates, etc.) directly usable for determining the state of vigilance of
the driver.

[0022] In addition, the data collected also include, as shown in FIG. 1,
the durations T1 and T2 of the temporal windows corresponding to the
maximum ratio calculated, and these data can also constitute parameters
for refining and improving the interpretation of the results.